Thrixspermum Lour. is a rather big genus (more 100 species) of the Orchid family, distributed from Sri Lanka, India to Pacific islands. It consists of 15 species in Vietnam. Thrixspermum species are herbs, epiphytic, lithophytic, monopodial, medium-sized. Stems ascending, climbing or pendulous. Leaves flat, never terete or laterally compressed, sometimes fleshy, base sheathing. Inflorescence lateral, axillary, racemose. Flowers usually ephemeral, often fully open for only half a day, small to medium-sized, very variable, from a few millimeters to several centimeters in diam. Sepals and petals subsimilar; lip adnate at base to end of column foot, immovable, saccate but not truly spurred, usually with a partly hairy or papillose, 3-lobed; lateral lobes erect; mid-lobe rather thick and fleshy. Column short, stout, with a long foot; pollinia waxy, 4, appearing as 2 unequal masses, subglobose, attached by a common short and broad stipe to a solitary viscidium. Capsule long, slender. Based on morphological characteristics of the genus Thrixspermum in Vietnam, the authors built the key to identify all species of the genus. Other informations such as botanical nomenclatures, sited literatures, types, distribution, diagnostic features are supplied in the article.
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